Tube making process



Feb. 17, I953 P. H. BRACE TUBE MAKING PROCESS 2 SHEETS-SHEET 1 Filed July 9, 1949 ENVENTOR f. H. BE/QCE Q WW ATTORNEY Feb. 17, 1953 P. H. BRACE TUBE MAKING PROCESS 2 SHEETS-SHEET 2 Filed July 9, 1949 INVENTOR H. B/E'HCE W umhwz ATTORNEY Patented Feb. 17, 1953 UNITED STATES ATENT OFFICE .TUBE MAKINGPROCESS 'Porter"H.'Brace, Forest Hills Boro, Pa., assignor "to "Westinghouse "Electric Corporation, East Pittsburgh, Pa, acorporation of Pennsylvania Application July 9, 1949,-Serial,No..103,846

.This application is a continuationein partof my application, Serial No.755.5,971, filedseptember27, 1944, and now abandoned.

This invention .relates .to the manufacture of tubes and. more particularly to such. ofthe. more refractory vmetals which develop mechanical anisotrophy, notably molybdenum and tungsten.

The principal object of myinvention, generally considered, is to provide tubing with high bursting strength, especially .of refractory metals which develop .mechanical anisotrophy and which are,;therefore, wrought in such a manner as .to provide circumferential or peripheral grain elongation, that is such at angles to radii of the tubing.

Another ,objectotmy inventionis to provide -a method .of working metals by radially forcing hollow articles .thereofinto dies .of varying .crosssectional shapes so as toelongate the grainstructure circumferentially.

A further object of my invention is to manufacture tubing with circumferential grain elongationcomprisingrexpanding a hollow billetin a die cavity of ashape differentlfrom the .outer contour of..said'bi1let (or as an alternative, compressing such .a billet about .a mandrel .by die members having engaging. surfaces .shaped differently from that. of the billet) then expanding the deformed billet \in .a die cavityof adiiferent shape (or if the alternative .is followed, again compressing such a billet about a .mandrel by .die members having engaging. surfaces shaped differently from thatofsaidbillet) .andlso on until a tubeof .the desiredsize and shape. is produced.

A still further object of my invention is to manufacture tubing by first ,placing'a hollow cylindrical or .prismatic billet, .while heated to working temperature, in .a die blockwcavity :of different cross-sectional shape, thatis, polygonal or circular :in cross section, as the-case may be, expanding it by a tapered mandrel to quickly drive therplastic metal outward to fill the die cavity, removing the. prismatic or cylindrical billet -.so formed again placing it in a die block cavity of different cross-sectional shape, that-is,

circular onpolygonal incrossesection, as the case may baagain expandingit-bya mandrel to fill said' cavity, and alternating with the polygonal and circular die cavities until tubing of the desired size. is produced.

Other objects and advantages of the invention, relating. to theparticular arrangement and construction .of the various parts, will become :apparent. as .the description proceeds.

,Referring tothe drawings:

Figures 1 .ShOWSiIl axialsection, a-die block of polygonal cross section within which is a hollow cylindrical billet having an outside diameter slightly less than that of the circle inscribed in the polygon representing the diecavity, a tapered mandrel being shown in the process of entering the billet.

Figure 2 is a transverse sectional-view-ofthe line II-II of Figure l, in thedirection-of the arrows.

Figure '.2 is a'view corresponding-to Figure32, but showing 'in section, a modification "of -the mandrel thereof to a larger scale.

'Figure'B is a'view similar to Figure -2,"but showing the parts after the mandrel has expanded the billet to .the "size of the (die cavity.

Figure-l is aview similar to Figure '2, but showing the billet, formedas in Figure -3, removed fromthedie thereof and placedin'a die having-a cylindrical cavity for subsequent Working.

Figure 5 is aview correspondingto Figure l, but showing the billet after the'same has been expanded in the cylindrical die cavity, as by forcing :a tapered mandrel *thereinto.

Figure 6 is aview corresponding to Figure 2, but showing analternative form of die into which a cylindrical billet is tube-expanded.

Figure 7 is aview of analternative apparatus in which a prismatic'billet isto be squeezedto cylindrical form abouta mandrel.

Figure 8 is a view correspondingto Figurefl, but showing the billet after having been squeezed to cylindrical form, .the .die portions removed therefrom, and the next setof -differently-shaped die portionspositionedforthe next operation.

"Figure 9 isa sectional view of a long-'throated die in which. a prismatic billetis being forced'by a mandrel to thereby get both circumferential and axial metal flow.

Figure 10 .isa view corresponding to Figure 9, butshowing the employment of a short-throated die, whereby the proportion of axialflow, as compared with circumferential. flow, is increased.

Figure 11. is anaxial sectional view, .with parts in side elevation, of apparatus for making .long tubes using .a draw "bar. andexpansion head. .enclosed in a thin. walled metal slip tube.

,Figure 12 isa transversev sectional view onthe line XIIXII of Figurell, in the-directionpf the arrows.

Figure 13 is a perspective view'of .aportionlof atube manufactured in accordancewith my invention.

- Certain. of the more refractory metals, notably molybdenum and tungsten, are obtainable in large masses only by powder metallurgy processes, that is, by compacting and sintering the metals in powdered form, such as may have been obtained by gaseous reduction of their oxides.

The billets as sintered may have considerable strength but at ordinary temperatures they are quite brittle and not well adapted to mechanical application.

By forging, swaging and rolling, commencing at temperatures generally in excess of l000 0., or between 1000 C. and 1500 0., when molybdenum is being manufactured, and generally in excess of 1200 C., or between 1200 C. and 1750" C. for tungsten, the sintered billets may be compacted, inter-crystalline bonding completed, and grain growth and grain elongation brought about, with the result that ductility is developed to a useful degree and acceptable mechanical properties obtained.

Tubing, for example, of molybdenum or tungsten, can be made by drilling wrought bars and swaging or drawing these blanks over mandrels to elongate them and correspondingly reduce the wall thickness to the desired extent. However, because molybdenum and tungsten develop mechanical anisotrophy, this kind of working produces tubing with only its axial strength due to the effected grain elongation strongly developed. In consequence, the circumferential mechanical strength and ductility are both relatively low, so that such tubing is of little use for high pressure applications.

In order to provide such wrought tubing with circumferential grain elongation and improved resistance to bursting stresses, I propose the following sequence of operations, commencing with relatively-thick walled tubes prepared by drilling billets or wrought bars, or by hot piercing or inverse extrustion of wrought billets. Although my process is particularly adaptable for manufacture of tubes of molybdenum, I do not wish to be limited to this metal as other anisotrophic metals such as tungsten, may be similarly treated. Therefore, in this specification and in the claims, the words, the group consisting of molybdenum and tungsten and like expressions, do not exclude alloys in which the proportion of the metal or metals incorporated with the molybdenum, tungsten, or alloy of such metals, is not large. enough to substantially affect the anisotrophic characteristics or impair the working properties.

I desirably start with a hollow cylindrical billet 2I, although one of prismatic or non cylindrical shape may be substituted, if desired. The billet may be of molybdenum produced in any desired manner, as by powder metallurgy, but preferably in accordance with the teachings of the Hall et al. Patent No. 2,431,690, dated December 2, 1947. The billet 2| is introduced into a die 22 having a cavity different in cross-section from the outer cross-section of the billet. For example, if the billet 2| is cylindrical, the die 22 has a cavity 23 different in cross-section, in this instance being shown as a polygon, specifically a square. Of course, if a billet prismatic in shape is started with, as in Figures 11 and 12, then the die cavity may be cylindrical, as in Figure 4, that is, circular in cross-section, or other shape different from the particular prismatic shape of the billet.

The die or mold 22 is shown resting on a supporting table or block 24, desirably apertured as indicated at 30, and the billet 2| is assumed to be at a working temperature, say, between approximately 1000 and 1400 C. if formed of molybdenum. A suitable mandrel 25 is quickly forced into the hollow interior 26 of the billet 2| and the aperture 30, causing the billet, which initially has a diameter only slightly less than that of the circle inscribed within the polygon representing the mold cavity, to expand in the mold 22, as illustrated in Figure 3, so that it flows laterally and more or less completely fills the cavity space 23, thus causing metal thereof to flow and be worked in the directions of the arrows, that is, toward the corners of the die, forming longitudinal thickenings at such locations. Such treatment involves a consequent circumferential grain elongation of the metal, and forms the billet 40 of a difierent shape.

The extent of working during a single cycle of operation will range from approximately 10% at the start while the billet is tender 1. e. likely to fail by tensile fracture, to 30% during later stages after some degree of circumferential fibering has developed and, concomitantly, a higher degree of plasticity.

Although the mandrel shown by Figure 1 con-. sists of a single, tapered bar circular in section, it may advantageously consist of a series of segments free to move radially under the impulse of a coaxial tapered wedging member'as illustrated in Figure 2 where 25 is the entire modi-' fied mandrel and 55 represents the tapered wedging member and 56 the corresponding segments that are forced radially outward when the wedging member is forced axially in the appropriate direction.

The next step in the process is to remove the billet 40, which is now square or other different shape in sectional outline, while still having a circular but enlarged bore. In order to facilitate removal of the billet from the die 22, the latter, as well as other dies for working such billets, may be slightly tapered. axially.

After removal and reheating to the working temperature desired, the prismatic billet Ml is then placed in a die or mold 26 having a cavity of diiferent shape, such as a cylindrical cavity 21, the diameter of the cavity being desirably only slightly greater than a miximum diameter of said prismatic billet. A mandrel 28 is then quickly forced into the prismatic billet 40, so that it is again expanded, this time to approach the hollow cylindrical form, as indicated at 50 in Figure 5. The process described in connection with Figures 2 and 3 may then be repeated, and alternated with that described in connection with Figures 4 and 5, until the pipe 50, illustrated in Figure 13, has the desired lengthand wall thickness. As the tube wall becomes thinner, the number of sides of the die cavity should be increased. 7

An alternative form is illustrated in Figure 6. in which the die 22 instead of having a truly prismatic cavity, or one square'in cross section, has a cavity 23 which is approximately square, but the walls thereof are curved rather than straight, as illustrated; The use of this kind of cavity for the reception of a billet 2P results in a greater working per step, while at the same time avoiding the formation of billets with sharp edges or corners. This type of cavity enables deformation to be effected with lower radial forces than with fiat-sided cavities. I

Figure 7 illustrates apparatus for effecting working by alternative means, that is, the die 22 is shown in two parts, designated respectively 29 and 3|, forming when closed a generally cylindrical cavity 32, in 'Which'a billet 21 prismatic in shape isshown. "In this instance, the billetis shown having a hexagonal "cross section and a hollow "mandrel 33 is disposed therewithin 'and'sep'arated therefromby a lubricated film or sheet 34. The mandrel 33 is hollow to allow for circulation of a cooling fluid such as water. In this instance, the working is'effected by forcing the die portions '29 and 3| together about the heated billet 21 or by forcing the tapered mandrel 33 thereinto, or both operations may occur simultaneously or sequentially, resulting in the formation of a cylindrical billet or pipe 24 as shown in FigureB.

' The next ste in the process, analogous to.

"wise as-employed in the preceding operation may be used.

In this instance, the working is effected by forcing the die portions 29 and 3| together about the heated billet 24 9, or by forcing the mandrel "33, if tapered, thereinto, or both operations may occur simultaneously or sequentially, resulting in the formation of aprismatic billet corresponding with that designated '40 in Figures 3 and 4.

The process described in connection with Figure '7 may then be repeated, and alternated with that described in connection with Figure 8, until a pipe or tube such as illustrated in Figure 13 is produced, which has the desired length and wall thickness. In other words, the process described in connection with Figures '7 and 8 is just the opposite of that of Figures 1 to 6, inclusive, in that the working is effected by force exertion and compression from the outside in, with or without expansion from the inside out, rather than mere force exertion and expansion from the inside out.

The two procedures, have, however, the common feature, that is, the important feature of my invention, namely, that lateral, plastic flow of the billet material is produced and, in consequence, the circumferential strength and ductility of the wrought tube increased.

Alternatively or in conjunction with procedures described above, other kinds of swaging may be resorted to for inducing circumferential flow together with more or less axial elongation.

For example a prismatic billet may be swaged over a round mandrel which may be watercooled to preserve its strength and thermally separated from the billet to conserve the temperature of the latter and to facilitate the removal of the mandrel after swaging. Or a prismatic billet is converted to a circular one by tangential flow from corner regions.

The proportion of circumferential to axial flow during the working process may be regulated by the design of the swaging die or mold. With a long-throated die 35, as shown in Figure 9, where the approach distance 36 is great, compared with the radial distance 31 between the surface of the mandrel and the corners of the billet, most of the 110w will be tangential.

However, where garters frequency power. -A draw bar 43'with :expan sionhead 44 is enclosedina thin vVaIIed metaI slip tube 55, thrust'through'thezboreiof the billet, and attached to a draw head,Lthat is, -the movable head 'of the conventional draw lbenc'h. wane attached head 4'4 is then 'pulled through the sli'p tube 45, expanding thatand the 'billet .'39, e;nd

.causing circumferential flow of the? metal inthe billet, after which a corresponding change .in the die and continued working may be effected, as

.described hereinbefore. Itwill be .noted that as the billet is shown prismatic, that is, .squareiin exterior section, while the die AI is shown having a cylindrical cavity defined by an inner .tubedfi surrounded by the heating coil 42, the form fof the billet after working iscylindrical, (so that subsequent working, if any, involvesthezuserof a prismatic die, as inFigure;2.

The function of the slip tube 45 is to provide a relatively cool lubricated surface inwhich the expansion head 44 can slide'as it advances alo the bore of the billet 39. The slip tube may :be of thin-walled seamless steel and will then.'add

.little to the resistance encountered by the TEX- pansion head, by greatly minimizing friction and wear, as compared to that which would occur if the expansion head were to slide for a considerable distance along the bore of the heated billet.

The draw bar 43 may be hollow, as indicated at 41, to allow for oil 48 or other lubricant and coolant which flows out of apertures 49 into the annular space between the slip tube 45 and the draw bar 43, from whence it discharges as indicated at 5|.

While I have shown mandrels and dies for the most part with plane surfaces, I do not restrict my proposals to such. For example, I may use both dies and mandrels with surfaces having wavy curvatures, as shown in Figure 6, to minimize the area of contact between die and billet, thus reducing the radial forces required to induce circumferential flow, as well as increase the amount of working per die.

I also contemplate introducing fluid at high pressure into the bore of the billet, or more particularly into the annular space between drawbar and slip tube, to provide supplementary radial forces to minimize the duty on the expansionhead.

There is also the problem of maintaining the temperature of the billet while in the die. In addition to the use of the heating coil 42, I contemplate placing an insulating refractory lubricious coating on the die say, mica, graphite, oil, or a thin pre-formed sleeve of mica with inorganic bond, and passing current longitudinally through the billet to heat or to supplement that otherwise supplied.

From the foregoing disclosure, it will be seen that I have provided a method for producing seamless tubing with tangential fibre, and consequent superior ductility and strength in tangem tlal or circumferential directions. Although particularly directed to the production of tubing of molybdenum and tungsten, in which circumferential ductility has been developed to a useful degree in billets produced by the powder metallurgy process, I do not wish to be limited thereto, as other materials, such as where th billets are initially cast in shape, may be similarly worked. V

, I claim:

1. 'The steps in the method of making a tubular metallic member comprising enclosing a tube of compacted and sintered metal powder, while the same is heated to working temperature, for its full length in a die of generally polygonal crosssection, passing a tapered mandrel through said tube to expand it to fill the de, removing the expanded tube, enclosing said tube,- while heated to working temperature, for its full length in another die of generally circular cross-section, and passing another tapered mandrel through said tube to expand it to fill the generally circular die.

2. The method of making a member of molybdenum comprisingfenclosing a tube of compacted and sintered molybdenum powder, while the same is heated to between 1000 C. and 1500 C., for its full length in a, die of generally polygonal crosssection, passing a tapered mandrel through said tube to expand it to fill the die, removing the expanded tube, enclosing said tube, while heated to between 1000 C..and 1500 C., for its full length in a die of generally circular cross-section, and passing another tapered mandrel through said expanded tube to further expand it to fill the generally circular die.

3. The method of making a member of tungsten comprising enclosing a tube of compacted and sintered tungsten powder, while the same is heated to between 1200" C. and 1750 C., for its full length in a die of generally polygonal crosssection, passing a tapered mandrel through said tube to expand it to fill the die, removing the expanded tube, enclosing said tube, while heated to between 1200 C. and 1750 0., for its full length in a die of generally circular cross-section, and passing another tapered mandrel through said expanded tube to further expand it to fill the generally circular die.

PORTER H. BRACE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name 7 Date 495,245 Ehrhardt Apr. 11, 1893 1,082,933 Coolidge Dec. 30, 1913 1,236,384 Fahrenwald Aug. 7, 1917 1,258,188 Cleveland Mar. 5, 1918 1,343,946 Warner June 22, 1920' 1,552,848 Langenberg Sept. 8, 1925 2,300,353 Eberhandt Oct. 27, 1942 2,373,405 Lowit Apr. 10, 1945 FOREIGN PATENTS Number Country Date 8,709 Great Britain Apr. 24, 1896 365,076 Germany Dec. 9, 1922 OTHER REFERENCES Powder Metallurgy by Paul Schwarzkopf, The MacMillan Company, New York, 1947. 

